alamb opened a new issue, #7907:
URL: https://github.com/apache/arrow-rs/issues/7907
**Describe the bug**
While writing tests for another feature, I hit a panic appending nested
objects th the Variant Builder
**To Reproduce**
Here are some tests that run in `parquet-variant/src/builder.rs`:
```rust
/// Test appending nested structures
#[test]
fn test_append_list() {
let (m1, v1) = make_list();
let variant = Variant::new(&m1, &v1);
let mut builder = VariantBuilder::new();
builder.append_value(variant.clone());
let (metadata, value) = builder.finish();
assert_eq!(variant, Variant::new(&metadata, &value));
}
/// make a simple List variant
fn make_list() -> (Vec<u8>, Vec<u8>) {
let mut builder = VariantBuilder::new();
let mut list = builder.new_list();
list.append_value(1234);
list.append_value("a string value");
list.finish();
builder.finish()
}
```
Teset for object
```rust
#[test]
fn test_append_object() {
let (m1, v1) = make_object();
let variant = Variant::new(&m1, &v1);
let mut builder = VariantBuilder::new();
builder.append_value(variant.clone());
let (metadata, value) = builder.finish();
assert_eq!(variant, Variant::new(&metadata, &value));
}
/// make an object variant
fn make_object() -> (Vec<u8>, Vec<u8>) {
let mut builder = VariantBuilder::new();
let mut obj = builder.new_object();
obj.insert("a", true);
obj.finish().unwrap();
builder.finish()
}
```
Both tests panic
```
internal error: entered unreachable code: Nested values are handled
specially by ObjectBuilder and ListBuilder
thread 'builder::tests::test_append_object' panicked at
parquet-variant/src/builder.rs:229:17:
internal error: entered unreachable code: Nested values are handled
specially by ObjectBuilder and ListBuilder
stack backtrace:
````
**Expected behavior**
I expect the tests to pass
**Additional context**
I don't think the builder can simply copy the underlying bytes directly into
its output buffer in the general case because field ids of any embedded objects
need to be updated to the in progress metadata
So the first implementation probably needs to walk over the nested
structures and append to the builder
Some future optimization could be to recognize when there are no embedded
objects and in that case just copy the bytes
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